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Add notion of a "transform function" that can simplify function calls.

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Initially, we use this only to eliminate calls to the varchar()
function in cases where the length is not being reduced and, therefore,
the function call is equivalent to a RelabelType operation.  The most
significant effect of this is that we can avoid a table rewrite when
changing a varchar(X) column to a varchar(Y) column, where Y > X.

Noah Misch, reviewed by me and Alexey Klyukin
This commit is contained in:
Robert Haas
2011-06-21 22:15:24 -04:00
parent 771a9f69f7
commit 8f9fe6edce
11 changed files with 2401 additions and 2280 deletions
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9
src/backend/commands/tablecmds.c
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@ -56,6 +56,7 @@
#include "nodes/nodeFuncs.h"
#include "nodes/parsenodes.h"
#include "optimizer/clauses.h"
#include "optimizer/planner.h"
#include "parser/parse_clause.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
@ -3495,7 +3496,8 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
{
NewColumnValue *ex = lfirst(l);
ex->exprstate = ExecPrepareExpr((Expr *) ex->expr, estate);
/* expr already planned */
ex->exprstate = ExecInitExpr((Expr *) ex->expr, NULL);
}
notnull_attrs = NIL;
@ -4398,7 +4400,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
newval = (NewColumnValue *) palloc0(sizeof(NewColumnValue));
newval->attnum = attribute.attnum;
newval->expr = defval;
newval->expr = expression_planner(defval);
tab->newvals = lappend(tab->newvals, newval);
tab->rewrite = true;
@ -6707,6 +6709,9 @@ ATPrepAlterColumnType(List **wqueue,
/* Fix collations after all else */
assign_expr_collations(pstate, transform);
/* Plan the expr now so we can accurately assess the need to rewrite. */
transform = (Node *) expression_planner((Expr *) transform);
/*
* Add a work queue item to make ATRewriteTable update the column
* contents.